Set placeholder text color for text field and area

TODO.md

@@ -26,7 +26,6 @@
   - Verify big avatars aren't downloaded uselessly
 
 - UI
-  - Set an explicit placeholder text color for text field/area
   - Show error if uploading avatar fails or file is corrupted
   - Way to open context menus without a right mouse button
   - Room header descriptions: styled text

src/qml/Base/HScrollableTextArea.qml

@@ -30,6 +30,7 @@ ScrollView {
         font.pixelSize: theme.fontSize.normal
         font.pointSize: -1
 
+        placeholderTextColor: theme.controls.textArea.placeholderText
         color: theme.controls.textArea.text
         background: Rectangle {
             id: textAreaBackground

src/qml/Base/HTextField.qml

@@ -24,6 +24,7 @@ TextField {
     property color focusedBorderColor: _tf.focusedBorder
     property alias radius: textFieldBackground.radius
 
+    placeholderTextColor: _tf.placeholderText
     color: activeFocus ? _tf.focusedText : _tf.text
 
     background: Rectangle {

src/themes/Default.qpl

@@ -154,10 +154,12 @@ controls:
 
         color text:            colors.text
         color focusedText:     colors.text
+        color placeholderText: colors.dimText
 
     textArea:
         color background:      colors.inputBackground
         color text:            colors.text
+        color placeholderText: controls.textField.placeholderText
 
     toolTip:
         int delay:        500